This invention relates to thermally activated electron-emissive cathodes for electron guns used in television cathode ray picture tubes, and in particular to an improved method of assembling certain components of such cathodes.
As is well-known in the art, the cathode assembly comprises two basic parts as shown by FIG. 1. One part of the cathode assembly 10 is a tubular cap 12 in the form of a straight-sided cup on the closed end of which is subsequently applied a thin, thermally activated electron-emissive coating 14. The second part is the tubular shank 16 which is an open-ended hollow tube having an end 18 larger in diameter than the cap and as shown by FIG. 1, a narrow end 20 adapted to fit into the cup formed by cap 12. The electron-emissive coating 14 deposited on the cap 12 is caused to emit electrons by the heat produced by a pair of electrically energized filament wires 22 extending into the shank 16 and the cap 12.
Hand-assembly of the two basic parts presents a problem in manufacture because of the very small size of the parts. For example, the length of the shank 16 is 0.320 inch and the length of the cap 12 is 0.110 inch. The outside diameter of the first or larger end 18 of the shank 16 is 0.1 inch, and the outside diameter of the narrow, or distal end, is 0.075 inch. The outside diameter of the cap 12 is 0.086 inch. It will be seen that assembly of large quantities of such small parts by hand is very labor-intensive and production rates are necessarily low. Also, the parts are fragile and can easily be damaged by hand assembly.
Accordingly, the objective of the invention is to provide a method for mating the basic two parts of the cathode assembly 10 that substantially eliminates hand assembly while greatly increasing the rate of assembly and reducing rejects.